Metalized ceramic members



G, l.. GALLET 3,265,473 METALIZED CERAMIC MEMERS or 1 Fued Aug. 1'?, 1959 igina Aug. 9, 1966 INVENTOR GEORGESLGALLET,

HIS ATTOR United 'States Patent O 3,265,473 METALZED CERAMIC MEMBERS Georges Louis Gallet, La Celie-St.-Cloud, France, assignor to Compagnie Francaise Thomson-Houston, Paris, France Original application Aug. 17, 1959, Ser. No. 834,034, now Patent No. 3,107,756, dated st. 22, 1963. Divided and this application Mar. 5, 1963, Ser. No. 268,849 3 Claims. (Cl. 29-195) This application is a division of application Serial No. 834,034, filed August 17, 11959, and now Patent No. `3,107,- 756, and commonly assigned herewith.

My invention relates to improved metalized ceramic members and improved means for effecting vacuum tight and high temperature resistant bonds between metallic and ceramic members.

In U.S. Patent No. 2,667,427 of Henry J. Nolte entitled, Method of Metalizing a Ceramic Member, and issued January 26, 1954, there is disclosed and claimed a Imethod of providing a closely adherent metallic surface on a ceramic member. The metallic surface comprises a highly refractory metal such as molybdenum tightly held to the ceramic by a liquid layer of a manganese modified composition which is formed on the surface of the ceramic body during sintering and which serves to strengthen t-he bond between the refractory metal and ceramic. The refractory metal layer serves as a metallic surface to which may be bonded or brazed a metal member or the metallic surface of another metalized ceramic member. Often the bond is effected using a nickel-containing or a copper-containing brazing alloy. Also, for some applications it has been found desirable to reinforce or thicken the refractory metal layer with the deposition, as by electroplating, of a second layer of material such as nickel or copper. This layer of metal is usually more readily wettable by the brazing alloy and serves as the surface to which a metal member or another metalized ceramic member may be brazed.

lI have found that during the mentioned brazing step a deterioration of the bond occurs between the refractory metal layer and the ceramic, thus adversely affecting adherence of the metalizing. This deterioration of the bond between the refractory metal layer and the ceramic results from solution of the refractory metal by the brazing alloy or wettable layer or destruction of the bond between the refractory metal particles and the ceramic substrate.

The Imentioned diffusion of nickel and copper through the refractory metal layer and the adverse effects thereof also -occur at the high temperatures at which some devices incorporating the described types of seals are normally operated With adverse effects on the vacuum tightness of the `brazed joints.

Accordingly, the primary object of my invention is to provide improved metalized ceramic structures.

Another object of my invention is to provide improved ceramic structures including tightly adhering refractory metalized surfaces and improved means for insuring continued tight adhesion of the metal material constituting the metalized surfaces.

Another and more specific object of my invention is to provide an improved metalized ceramic structure which is adapted -for resisting the deteriorating effects of nickel Aand copper on the strength of the bond between the metalized layer and ceramic material.

Another object of my invention is to provide improved vacuum-tight metallic bonds including improved means for insuring continued vacuum tightness thereof.

Another object of my invention is to provide improved metallic bonds effective for adapting devices incorporating same for high temperature operation.

Further objects and advantages of my invention will become apparent as the following description proceeds Patented August 9, 1966 ICC and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

The invention itself will be best understood from the following description when taken in connection with the accompanying drawing in which:

FIGURE 1 is a perspective view of a ceramic cylinder metalized at one end in accordance with one form of my invention;

FIGURE 2 is an enlarged fragmentary sectional view of the structure of FIGURE l;

FIGURE 3 is an enlarged fragmentary sectional view illustrating a seal between a ceramic member constructed according to my invention and a metal member;

FIGURE 4 is an enlarged fragmentary sectional view illustrating a seal between a pair of ceramic members constructed according to my invention; and

FIGURE 5 is an enlarged fragmentary sectional view illustrating a modified lform of my invention.

Illustrated in FIGURE 1 is a ceramic member l1 prepared according to an embodiment of my invention and wherein the metalized area comprises an annular outer surface portion 2. The ceramic material can be any one of the several types widely employed in electron tube manufacture such, for example, as the forsterite and alumina ceramics.

As better seen in FIGURE K2, the metalized area of the ceramic member 1 comprises a metallic layer 3 of particles of highly refractory metal which can be any one of the metals selected from .the group including molybdenum, tungsten and iron but which preferably is molybdenum. The metallic layer 3 comprising the refractory metal particles can be applied to the ceramic in the manner described in the above-identified Nolte patent and is strongly adhered or bonded to the ceramic material by a manganese modified bonding composition 4 which is formed during the sintering step whereby the layer 3 is adhered to the ceramic. It will be understood that in FIGURES 3 through 5 the thicknesses of the various layers of material are illustrated exaggeratedly IIn actuality these layers will 'be` very thin, the prescribed thicknesses being set forth Ibelow.

Provided on the outer surface of the refractory metal layer -3 is a layer 5 of metal selected from the group including rhodium, platinum and iridiurn and alloys thereof. The layer 5 may be applied to the layer 3 in any suitable manner.'

`Formed over rthe layer 5 is a layer 6 of metal selected from the group including nickel and copper and alloys thereof. The layer 6 is provided to afford a metal surface which is readily wettable by a solder material which is shown as a layer designated 7 in FIGURE 3 and which is adapted for bonding another member such as a metal sleeve or envelope section 8 to the metalized area of the ceramic section.

The solder material 7 can be any suitable commercially available solder material and can be a nickel-containing or copper-containing brazing alloy such, for example, as nickel-gold alloys which have been found particularly effective in making the necessary Ibrazed joint.

As indicated above, I have found that when the solderwettable layer 6 comprises nickel or copper or any alloy containing one of these metals or when the brazing alloy contains nickel or copper, these materials tend, during the brazing process or at high operating temperatures of a device incorporating the disclosed type of seal, to diffuse .through or penetrate the refractory metal layer 3 and attack or detrimentally affect the bonding material 4 between the refractory metal and the ceramic material. This diffusion or penetration is cause-d by the high temperature to which the materials are raised during the brazing process and especially during long brazing cycles;

and the detrimental effects resulting involve the destruction of the previously accomplished tight adhesion of the layer 3. Additionally, the mentioned difficulty and undesirable effects on the adhesion on the layer 3 tend to be encountered when the seals are incorporated in devices adapted for normal operation at high temperatures. Thus, the adaptability of the device for high temperature operation is adversely affected. My invention is particularly effective in adapting devices for high temperature operation.

According `to my invention the metals selected from the group including rhodium, platinum and iridiurn and combinations thereof constitute the layer 5. These metals have negibilibly solid solubidity in the refractory metal constituting the layer 3.

Thus, upon heating, as during brazing, or tube operation, .there is negligible mutual solution of the material of the refractory metal layer and the material of the group including rhodium, platinum and iridium. As a result, the nickel and copper are prevented from attacking or adversely affecting the bonding material between the -refractory metal layer 3 and the ceramic 1.

I have found the use of molybdenum as the refractory metal layer and the use of rhodium thereon particularly effective due to the negligible low solubility of rhodium in molybdenum -and the low solubility of molybdenum in rhodium. Additionally, I have found rhodium highly desirable because of its adaptability for being deposited easily by electroplating and its effectiveness in providing thereby a vacuum-tight highly adherent layer of film. Also, rhodium has a low vapor pressure which is highly desirable in materials used in electron tube manufacture.

Additionally, I have found highly satisfactory ceramic structures made according to my invention when the refractory metal layer has had a thickness between approximately 15 and approximately 50 microns, the layer 5 of rhodium has been between approximately 0.5 and approximately 2 microns and the layer 6 of nickel and copper or alloys of these materials has not exceeded 20 microns.

Illustrated in FIGURE 4 are a pair of ceramic members 10 having the abutting end surfaces thereof each metalized to include the several layers of metal described above and illustrated in FIGURE 2. The same designations are utilized in FIGURE 4 to indicate layers of material identical to those provided in the structure of FIGURE 2. The solder '7 in the structure of FIGURE 4, however, serves to join the layers 6 of both ceramic members which, in turn, are deposited on rhodium layers 5,-which are deposited on the refractory metal layers 3 which are bonded by the modified manganese substance or to the members 10.

As indicated above, it is desirable to adapt some devices for high temperature applications. Illustrated in FIG- URE is a seal constructed according to a form of my invention and adapted for resisting high temperatures. In this embodiment a ceramic member 11 is provided with a refractory metal layer 12 formed of one of the above-disclosed materials and preferably molybdenum. The layer 12 is bonded to the ceramic by a manganese modified substance 13 formed during sintering. Provided on the layer 12 is a film or layer 14 of material selected from the group including rhodium, platinum, iridium and lcombinations thereof. On the film 14 is provided a layer or lm of gold 15 and used to effect a bond between the gold layer 15 and a metal section 16 is a nickel-gold eutectic brazing alloy 17. This type of joint is, because of the high brazing temperature of nickel-gold alloys `above about 950 C., particularly effective for withstanding high temperatures in addition to avoiding diffusion of the nickel in the solder to the bonding material 13 which would result in detrimental effects to the adhesion of the metalized surface. Alternatively, gold-copper alloys may be employable in similar seals.

It will be understood from the foregoing that my invention is adapted for avoiding the diffusion or penetration of copper and nickel through a layer of refractory metal bonded to the surface of a ceramic member, thus to avoid detrimental effects `on the bond between the refractory metal layer and the ceramic and thus on the metalization as a whole. The nickel and copper prevented from diffusing through the layer of refractory metal can originate as a solder wettable layer containing one or more of these materials provided on the surface of the refractory metal or can be contained in solder material used to effect bonds to other metal or metalized ceramic members. Additionally, the modified embodiment -of my invention illustrated in FIGURE 5 is adapted for avoiding the abovedescribed detrimental effects of the mentioned materials while also adapting a device incorporating the improved seal for higher operating temperatures.

While I have shown and described specific embodiments of my invention I do not desire my invention to be limited to the particular forms shown and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent is:

1. A metalized ceramic structure comprising a ceramic body, a metalized layer of highly refractory metal bonded to said ceramic body, a layer of material selected from the group including rhodium, platinum and iridium and combinations thereof on said refractory metal, and an outer layer of gold. Y

2. A metal-ized ceramic structure according to claim 1, wherein said outer layer of gold has a thickness lbetween approximately 10 and approximately 15 microns.

3. A metalized ceramic structure comprising a ceramic body, a layer of molybdenum bonded to a surface of said ceramic body, a layer of rhodium on said layer of molybdenum, and a layer of gold yon said rhodium, whereby said structure is adapted for being brazed to another member with a nickel-gold solder material to effect a high temperature resistance seal and in which detrimental effects of the nickel in said solder material on said bond between said molybdenum and said ceramic are avoided.

No references cited.

HYLAND BIZOT, Primary Examiner. 

1. A METALIZED CERAMIC STRUCTURE COMPRISING A CERAMIC BODY, A METALIZED LAYER OF HIGHLY REFRACTORY METAL BONDED TO SAID CERAMIC BODY, A LAYER OF MATERIAL SELECTED FROM THE GROUP INCLUDING RHODIUM, PLATINUM AND IRIDIUM AND COMBINATIONS THEREOF ON SAID REFRACTORY METAL, AND AN OUTER LAYER OF GOLD. 